Performs a bulk comparison of two records (source and
target) by comparing source and target fields of the same name for
equality and storing the result in a field. You can specify a list
of fields to exclude, or a list of fields to include. You can also
specify WHEN...THEN phrases. For all such phrases you specify, the
AVM evaluates the WHEN portion, and if it evaluates to TRUE, the
AVM executes the THEN portion.
Syntax
BUFFER-COMPARE source
[ { EXCEPT | USING } field ... ] TO target
[ CASE-SENSITIVE | BINARY ]
[ SAVE [ RESULT IN ] result-field ]
[ [ EXPLICIT ] COMPARES ]:
[ WHEN field compare-operator expression
THEN statement-or-block ] ...
[ END [ COMPARES ] ] [ NO-LOBS ] [ NO-ERROR ]
|
-
source
- The source database table, buffer, temp-table, or work table.
- EXCEPT field
- A list of source fields to exclude from the bulk compare.
- USING field
- A list of source fields to include in the bulk compare. The
USING option is a positive version of the EXCEPT option.
- TO target
- The target database table, buffer, temp-table, or work table.
- CASE-SENSITIVE
- Directs the AVM to perform a case-sensitive comparison.
- BINARY
- Directs the AVM to perform a binary comparison.
- SAVE RESULT IN result-field
- A variable or field to contain the result of the comparison.
The variable or field must be CHARACTER or LOGICAL.
If result-field is
CHARACTER, the result is a comma-separated list of fields that failed
the comparison, sorted in ascending order.
If result-field is
LOGICAL, the result is YES if all fields are equal, or NO if any
fields are unequal. In either case, BUFFER-COMPARE stops comparing
when it encounters the first inequality.
- EXPLICIT COMPARES
- Opens a block of WHEN options. If you open the block, you must close
it with END COMPARES.
- WHEN field
- Any data field in the source.
BUFFER-COMPARE removes this
field from a USING list or adds this field to an EXCEPT list. This
removes the field from the bulk compare and from result-field.
-
compare-operator
- Represents one of the following: LT, LE, GT, GE, EQ, NE, MATCHES,
BEGINS, or CONTAINS.
Note: For BLOB or CLOB fields,
you can only use the EQ (=) or NE (<>) operators.
-
expression
- Any valid ABL expression.
- THEN statement-or-block
- Any ABL statement or block. The statement or block executes
when the WHEN clause evaluates to TRUE.
- END COMPARES
- Closes the block of WHEN phrases.
- NO-LOBS
- Directs the AVM to ignore large object data when comparing records that contain BLOB
or CLOB fields.
Caution:
When using this option, you get no warning if a LOB
field has changed. This can lead to inappropriate results. Therefore, before using
this option, you must understand the nature of your data and be sure that logic using
this option will not result in inconsistent or out-of-date data in the
database.
- NO-ERROR
- Suppresses ABL errors or error messages that would otherwise occur and diverts them to
the ERROR-STATUS system handle. If an error occurs, the
action of the statement is not done and execution continues with the next statement. If
the statement fails, any persistent side-effects of the statement are backed out. If the
statement includes an expression that contains other executable elements, like methods,
the work performed by these elements may or may not be done, depending on the order the
AVM resolves the expression elements and the occurrence of the error.
To check for
errors after a statement that uses the NO-ERROR option:
- Check the ERROR-STATUS:ERROR attribute to see if the AVM raised the ERROR
condition.
- Check if the ERROR-STATUS:NUM-MESSAGES attribute is greater than zero to see if
the AVM generated error messages. ABL handle methods used in a block without
a CATCH end block treat errors as warnings and do not raise ERROR, do not set the
ERROR-STATUS:ERROR attribute, but do add messages to the ERROR-STATUS system handle.
Therefore, this test is the better test for code using handle methods without CATCH
end blocks. ABL handle methods used in a block with a CATCH end block raise
ERROR and add messages to the error object generated by the AVM. In this case, the
AVM does not update the ERROR-STATUS system handle.
- Use ERROR-STATUS:GET-MESSAGE( message-num ) to retrieve a
particular message, where message-num is 1 for the first
message.
If the statement does not include the NO-ERROR option, you can use a CATCH end
block to handle errors raised by the statement.
Some other important usage notes
on the NO-ERROR option:
- NO-ERROR does not suppress errors that raise the STOP or QUIT condition.
- A CATCH statement, which introduces a CATCH end block, is analogous to a NO-ERROR
option in that it also suppresses errors, but it does so for an entire block of
code. It is different in that the error messages are contained in a class-based
error object (generated by the AVM or explicitly thrown), as opposed to the
ERROR-STATUS system handle. Also, if errors raised in the block are not handled by a
compatible CATCH block, ON ERROR phrase, or UNDO statement, then the error is not
suppressed, but handled with the default error processing for that block type.
- When a statement contains the NO-ERROR option and resides in a block with a CATCH
end block, the NO-ERROR option takes precedence over the CATCH block. That is, an
error raised on the statement with the NO-ERROR option will not be handled by a
compatible CATCH end block. The error is redirected to the ERROR-STATUS system
handle as normal.
- If an error object is thrown to a statement that includes the NO-ERROR option,
then the information and messages in the error object will be used to set the
ERROR-STATUS system handle. This interoperability feature is important for those
integrating code that uses the traditional NO-ERROR technique with the newer,
structured error handling that features error objects and CATCH end blocks.
